This invention relates to a method and apparatus for lifting a pair of wheels of a tandem rear axle truck trailer selectively to reduce the wear on those wheels and the associated brakes when the load in the trailer has been removed.
Large truck trailers, such as those that are designed to carry large cargo loads along roadways, generally have tandem axles at least in the rear of the trailer. So called xe2x80x9c18-wheelers,xe2x80x9d for example, have a pair of rear tandem axles each carrying four wheels and tires. The load on each axle is thereby divided among the two rear axles and the front axle. This also places less load applied by any single axle to below the maximum permitted by federal highway bridge load regulations.
In such vehicles the multitude of tires carrying the load have an equal number of brakes which must be applied to the respective wheel to reduce the vehicle speed and stop the vehicle. Once the payload has been delivered, however, there is little reason to split the light loads at the rear of the trailer between two axles since this creates unnecessary wear on the tires and the brakes compared to having the load on only one of the axles. Thus, it would be desirable to reduce the wear on the tires and the brakes associated with one axle of the tandem pair, particularly the front axle of the rear tandem pair.
Consequently, it is a primary object of the present invention to provide a simple means for raising the front axle of a tandem axle truck trailer relative to the rear axle, thereby to lift the tires of the front axle off the roadway.
It is another object of the present invention to provide a simple means for pivoting a first axle of a tandem pair of axles relative to the other axle to lift the first axle thereby to lift the tires mounted thereon off the roadway.
It is a further object of the present invention to provide air bags intermediate the frame of a truck trailer and at least one axle of a tandem axle pair of the trailer, the axles being mounted in a suspension system about a pivot so that selective inflation of the bags may raise the one axle of the pair thereby to lift the tires mounted thereon off the road.
Accordingly, the present invention provides for a truck trailer having a pair of tandem spaced apart axles and a suspension system for supporting the axles from the chassis of the trailer which suspension system includes leaf springs connected to the axles and a pivot member intermediate the axles about which the leaf springs may pivot, apparatus for lifting one of the axles relative to the other selectively by applying a force which effects pivoting of the leaf springs about the pivot member so that the wheels carried by the lifted axle may be lifted off the roadway. The apparatus includes air bags which may be inflated or deflated to control the position of the axle to be raised. In the preferred embodiment the air bags are associated with one axle and are disposed intermediate the axle and the chassis, the air bags being inflatable to lift the other axle about the pivot member. Alternatively, the air bags may be associated with both axles and kept inflated until one axle is to be lifted, at which time the air bags associated with the other axle may be deflated.